Molecular characterization and relationship of methicillin-resistant Staphylococcus aureus among strains from healthy carriers and university hospital patients, southern Thailand.

Methicillin-resistant Staphylococcus aureus (MRSA) plays an important role in nosocomial infections including those in communities. MRSA enables colonization in the nares and throats of healthy people. In this study, investigation of MRSA prevalence from the throats of healthy subjects in southern Thailand revealed that among 153 isolates, 2 showed mecA+ genotype by PCR. One mecA+ isolate was susceptible to methicillin, indicating a cryptically methicillin-resistant strain. Antimicrobial susceptibility test demonstrated that 43% were resistant to erythromycin. More importantly, two isolates had the propensity of reduced susceptibility to vancomycin. Other virulence genes harbored by 2 and 8 MRSA from healthy carriers and hospitals, respectively, exhibited that 3 clinical strains possessed coagulase gene while von Willebrand factor binding protein gene was present in one clinical MRSA strain. Staphylococcal enterotoxin A gene was found in 2 clinical MRSA isolates and Panton-Valentine leukocidin gene in 3 S. aureus isolates. However, all MRSA in this study lacked Panton-Valentine leukocidin gene, suggesting that they were belonged to hospital-associated MRSA lineage. MRSA typing by repetitive-sequence PCR revealed distinguishable fingerprint patterns among the MRSA isolates from both healthy carriers and hospital patients, indicating the heterogeneity of their genetic elements and that the infections caused by MRSA in this area resulted from different clones. This demonstrated a wide variety of MRSA strains in the population of southern Thailand.